In food-cooking appliances, in particular deep flyers, it is known that when the food to be cooked is immersed in the oil or fat which is heated to a high temperature, chemical substances are released into the air, such substances having a strong, unpleasant, and distinctive odor characteristic of the flying operation proper. The chemical substances released into the air and responsible for the unpleasant odor are known and are mainly constituted by volatile organic compounds (VOCs), aldehydes, and acids.
Naturally, it is already known that various treatment means can be used for the purpose of preventing or treating the fumes that result from cooking food in such cooking appliances.
A first one of such known treatment means consists, naturally, in cooking the food in a closed atmosphere by implementing a suitably leaktight connection between the bowl and the lid of the appliance.
However, for obvious safety reasons, in particular in deep fryers in which, it is necessary to provide an exhaust outlet for the cooking fumes because of the large quantity of fumes generated by the food during frying (especially when potatoes are being fried), such appliances are equipped with means for treating cooking odors in order to rid the cooking fumes of all or some of the volatile molecules responsible for the cooking odor.
Various devices have been devised, and in particular it is known that activated carbon filters can be used that make it possible to retain all or some of the grease, as is described, for example, in Patent FR-1 568 985 or in Patent EP-150 516.
Unfortunately, in order to be effective, activated carbon filters in the cooking appliance must be changed frequently, which constitutes an additional design constraint for the appliance insofar as it is essential to make provision to design a system for fitting and removing the activated carbon filter. In addition, it is observed that the user frequently forgets to change the activated carbon filter, such an operation being perceived as a chore. The combination of all of those reasons makes the use of activated carbon filters ill-suited for treating cooking odors. In addition, they are not absolutely and universally effective and they also allow the stream of treated fumes discharged from the appliance to be seen.
A system for treating frying odors is also known that consists in condensing the cooking fumes in a condensation system mounted in the appliance. Such a system does not suffer from the drawbacks of having to change all or some of the system as is required for activated carbon filters, but it does require the user to perform a relatively tedious action each time a cooking operation is effected. The condensation system must be kept at a very low temperature, e.g. in a freezer, throughout the periods during which it is not in use, and it must then be fitted to the cooking appliance itself before any cooking operation. In addition, that system must then be emptied after the cooking operation. The requirement to make the system cold again prevents another cooking operation from being performed with the same system for 24 hours. This systematic fitting operation can be perceived by the user as an additional chore. Furthermore, condensation systems are generally large in volume, which constitutes a further design constraint insofar as it is necessary to integrate such a system into a cooking appliance whose size must generally be limited.
Finally it is already known that a catalytic converter can be used that is mounted in the lid of a deep fryer for the purpose of treating cooking odors. The use of catalytic converters avoids any specific action being necessary, unlike systems including activated carbon filters or condensation systems, because the catalytic converter is installed permanently in the appliance, and thus forms a permanent odor treatment unit.
Unfortunately, a catalytic converter that is to be integrated into a food-cooking appliance, and in particular into a deep fryer, is difficult to design, and known catalytic converters that are used in deep fryers are unsatisfactory, and indeed such use remains the exception.
Designing a catalytic converter that is to be integrated into a food-cooking appliance is made particularly difficult because of the need to keep the cooking appliance completely closed throughout a cooking cycle, which implies that no oxygen is admitted from the outside during one full cooking cycle, the cooking thus taking place in an atmosphere that is substantially closed, ignoring leaks.
That constraint implies firstly that all of the cooking fumes pass through the catalytic converter, and secondly that the catalytic converter is capable of reacting appropriately throughout the entire cooking cycle without any oxygen being admitted from the outside, and merely by making good use of the initial volume of fluid contained inside the cooking enclosure.
In addition, for greater effectiveness, the catalytic converter must be defined such that the fumes generated by the cooking can pass freely through the converter, without them passing therethrough at excessive speeds, precisely so as to ensure that the fumes are treated properly in the active portion of the catalytic converter proper.
Finally, it will be understood that catalytic converters designed for use in the household electrical field must satisfy conventional criteria of being reliable, low in cost, and long-lasting.